Desmosomes are cell-cell adhesion structures that are required for the mechanical strength of the epidermis. Disruption of desmosomes results in devastating effects on skin integrity in diseases including pemphigus vulgaris/foliaceus and some types of epidermolysis bullosa. Mutations in desmosomal proteins also lead to cardiomyopathies/dysplasias. Our long-term goal is to understand the assembly and functions of desmosomes and the cellular responses to their disruption. The canonical function of desmosomes is to physically link keratin networks between cells. While we have a good understanding of the direct physical interactions that mediate keratin attachment, it is not known whether desmosomes affect keratin assembly. We have identified a novel desmosomal protein with the unique ability to promote the local assembly of keratin filaments. This changes our view of desmosomes from relatively passive structures that simply bind cytoskeletal networks to active modulators of their assembly. We will study the mechanism and regulation of this remarkable activity, which is expected to identify a novel pathway for desmosome stability and epidermal integrity. Our second aim will use a targeted proteomics approach to identify novel and transiently associated desmosomal proteins. This will identify additional putative disease genes and allow future quantitative determination of changes in desmosome composition in various disease states. Finally, our third aim addresses cellular responses to loss of desmosomes. We have found that desmosome disruption leads to dramatic changes in adherens and tight junction activity through effects on protein expression and localization. We will determine how cells sense desmosome disruption and determine the signaling pathways that control alterations of other cell adhesion structures. In total, these studies will increase or understanding of normal desmosome function and cellular responses to their perturbation which we expect to yield diagnostic and therapeutic tools for desmosome-related diseases.